Some perspective needed in this thread. Not everything which looks difficult is necessarily a mystery.
Extremely large monoliths CAN be split using only simple tools. They are usually split using wedges or heat in prepared fracture lines, rather than cut. It is not a lost knowledge in the slightest.
Large monoliths CAN also be transported long distances over land and sea using relatively simple equipment and manpower. The largest single stone ever moved by humans was the Thunder Stone. It weighed 1500T (now 1250T) and was moved by the Russians in 1770. It was moved over land and sea without modern or sophisticated tools or machinery.
